This invention relates to a geothermal steam turbine plant and particularly to a gas ejecting system therefor for ejecting non-condensed gas from a main condenser.
A condenser for use in a goethermal steam turbine plant is generally classified into the direct-contact type and the indirect-contact type.
In the direct-contact type condenser, in which condensate water directly contacts cooling water, cooling water is sprayed and exhausted geothermal steam from a steam tubine is directly contacted with the sprayed cooling water to condense the steam thereby to obtain the condensate water. This is a so-called cooling system specific for the geothermal steam turbine plant which does not require the separation of the steam and the cooling water.
On the other hand, in the indirect-contact type condenser condensate water does not directly contact cooling water and in which cooling water circulates in heat exchanging tubes located in the condenser and the indirect heat exchanging process is performed between the cooling water and turbine exhaust steam through the heat exchanging tubes thereby to condense the steam.
Conventional geothermal steam turbine plants respectively utilizing the direct--and indirect--contact type condensers will be explained hereunder with reference to schematic diagrams shown in FIGS. 2 and 3.
Referring to FIG. 2 which shows the conventional geothermal steam turbine plant employing a direct-contact type condenser, reference numerals 1 and 2 designate a direct-contact type main condenser and a steam turbine, respectively. The geothermal steam supplied from a production well (W) through a main steam pipe 3 is fed to the steam turbine 2 to perform its function of driving a generator (not shown) therein and is exhausted into the main condenser 1. Within the main condenser 1, cooling water from a cooling water tower or vessel 4 is sprayed through a water distributor from a spray pipe 5 which is provided with a plurality of nozzles. The steam exhausted from the steam turbine 2 is contacted to the cooling water and then condensed into condensate, which is pooled at the bottom of the condenser 1.
The condensate pooled in the condenser 1 is then fed to the cooling water tower 4 by the operation of a condensate water pump 6 assembled in a pipe line extending outwardly from the bottom of the main condenser 1. The condensate in the cooling water tower 4 is cooled in direct contact to the atmosphere and then pooled in a water tank located at the bottom of the cooling water tower 4. In the illustrated example, the cooling water pooled in the water tank of the cooling water tower is vacuumed by means of the substantial vacuum condition in the main condenser 1 thereinto through the water distributor 5 and again used as cooling water in the main condenser 1.
Since non-condensed gases contained in the geothermal steam except for ones dissolved in the condensate are accummulated in the main condenser 1, the removal of the accummulated gases will be required. A mechanical extractor, for example a gas compressor, steam ejector or the like, is generally used as means for removing the non-condensed gases, and the example illustrated in FIG. 2 utilizes the steam jet ejector. Namely, the geothermal steam from the main steam pipe 3 is fed into first and second stage steam jet ejectors 7 and 8, respectively, whereby the non-condensed gases in the condenser 1 are sucked by the ejecting effect, and exhausted into the atmosphere.
Mixed fluid consisting of the non-condensed gasses and the steam exhausted from the first stage steam ejector 7 is fed to an inter condenser 9, in which the mixed fluid is cooled by the cooling water sprayed from a water distributor as a spray pipe 10 thereby to condense only the steam. As the cooling water for this use is used in the water sucked up through an auxiliary cooling water line from the water tank of the cooling water tower 4 by means of an auxiliary cooling water pump 11.
The goethermal water condensed in the inter condenser 9 is returned into the condenser 1 through a drain return pipe line 12. The non-condensed gases are sucked into the second stage steam jet ejector 8, in which the pressure of the gases are raised, together with operating steam, over the atmospheric pressure, and the gases are then fed into an after condenser 13, in which the cooling water fed through the auxiliary cooling water line from the auxiliary cooling water pump 11 is sprayed through a water distributor as a spray pipe 14. The steam is cooled and condensed by the cooling water sprayed through the water distributor 14, and the condensate water is then returned to the main condenser 1 through a drain return pipe line 15. The non-condensed gases in the after condenser 13 have a gas pressure, for example 1.05-1.1 ata, higher than the atmospheric pressure, so that the gases are exhausted into the atmosphere through an exhaust pipe 16 due to the pressure difference therebetween.
In the main condenser gas ejecting system having the structure described hereinabove, since the cooling air and the condensate fed by means of the condensate pump 6 are directly contacted in the cooling tower, the condensed water is evaporated into the air or removed by air as water drops. On the other hand, however, since the geothermal steam fed into the steam turbine 2, the inter condenser 9 and the after condenser 1 13 is condensed into condensate and then fed into the cooling system as cooling water, the cooling water in the whole system tends to increase. For this reason, the cooling water over the predetermined level in the water tank of the cooling water tower 4 is discharged outside the system through an over-flow pipe 17.
FIG. 3 shows an example of a system utilizing an indirect-contact type main condenser, in which reference numeral 1A designates an indirect-contact type main condenser which is provided with a number of condenser tubes 18, so that the production cost of the indirect contact type main condenser of the type 1A is high in comparison with that of the direct-contact type condenser as shown in FIG. 2. Because of this fact, in a geothermal steam turbine plant, the direct-contact type condenser is generally used.
In a case, however, where the direct-contact type main condenser is utilized, as described with reference to the example shown in FIG. 2, a portion of the geothermal steam is evaporated or mixed with the air to be dispersed into the atmosphere through the cooling water tower 4, and in another view point, the excessive geothermal water pooled in the water tank of the cooling water tower 4 is caused to overflow and discharged outside the system through an overflow pipe. The geothermal steam or water may sometimes contain various impurities some of which contain a harmful hydrogen sulphide (H.sub.2 S), and in such cases, the disposal of such harmful substances should be controlled or prescribed by law. Accordingly, in a case where there is a possibility for the disposal of the geothermal steam including harmful substances, it will be necessary to separate the system for processing the cooling water from the system for processing the geothermal steam in use of the indirect-contact type main condenser.
When the indirect-contact type main condenser 1A shown in FIG. 3 is utilized, an inter condenser 9A and an after condenser 13A are also constructed as indirect-contact type system, the condenser 1A, the inter condenser 9A and the after condenser 13A are provided with cooling tubes 18, 19 and 20, respectively, and the cooling water tower 4 is supplied by the operation of the cooling water circulation pump 21 into the main condenser 1A, the inter condenser 9A and the after condenser 13A through a circulating cooling water line. The heat exchanging operation between the cooling water and the steam is performed during the passing of the cooling water through the cooling tubes 18, 19 and 20, respectively, and after the heat exchanging process, the cooling water again returns to the cooling water tower 4, in which the water is cooled by air and again pooled in the water tank to reuse the same as the cooling water to be fed through the circulating cooling water line by means of the circulation pump 21.
As described hereinabove, in the system including the indirect-contact type main condenser 1A, since the cooling water circulation system constitutes an independent closed circulation cycle, the geothermal steam or water is never introduced into the cooling water. Due to this constructional fact, the cooling water can be completely separated from the geothermal water in use of fresh water such as river water or sea water. In this case, although a portion of the cooling water is of course discharged into the atmosphere with the air from the cooling water tower 4, the mixed air includes no harmful substance, thus providing no environmental problem.
An additional water supply pipe 17 is connected to the cooling water tower 4 for supplementing the cooling water evaporated or dispersed into the atmosphere, but all the geothermal water condensed in the inter condenser 9A and the after condenser 13A is returned to the main condenser 1A and mixed with the condensate from the steam turbine 2. The thus condensed and mixed geothermal water is then discharged into a re-injection well externally connected to the condensate pipe line 22 including the condensate water pump 6 to prevent the environmental pollution. It should be noted that equipments or members, shown in FIG. 3, designated by the same reference numerals as those of the first example shown in FIG. 2 are not explained in a repeated manner.
As described above, in the conventional systems, when the direct-contact type main condenser 1 is utilized, the inter condenser 9 and the after condenser 13 are also constructed as direct-contact types, and on the other hand, when the indirect-contact type main condenser 1A is utilized, the inter condenser 9A and the after condenser 13A are also constructed as indirect-contact types. In a case where the indirect-contact type system is utilized, the inter condenser 9A and the after condenser 13A are very enlarged, which results in higher production cost, since, relatively low heat exchanging efficiency will be attained. Namely, in the indirect-contact type system, the heat exchanging operation is performed between the mixed fluid, in the inter condenser 9A and the after condenser 13A, consisting of the steam and the non-condensed gasses and the cooling water passing through the cooling water tubes. However, because of the existence of the non-condensed gas, the heat exchanging efficiency is lowered, and for this reason, it is required to use cooling tubes having a surface area larger than that of tubes to be used for heat-exchanging and condensing only the steam. It is accordingly required to use an increased number of the cooling tubes, which results in the enlargement of the heat exchanging equipment, thus being not economical.
In the meantime, when the inter condenser 9 and the after condenser 13 of the direct-contact type are incorporated in the system utilizing the indirect-contact type condenser 1A, the geothermal water is mixed with the cooling water of fresh water in both condensers 9A and 13A. In this case, in order to avoid discharging the geothermal water outside the system, it is necessary to return the mixed condensate into the main condenser 1A and it should be discharged into the reinjection well. This, however, means that the cooling fresh water is continuously lost together with the geothermal water, which results in the defect that a fresh water amount to be supplemented into the cooling water tower 4 should be increased.